The present invention relates to papermaking felts and a method for forming high bulk and decorative paper. More particularly, the invention is directed toward patterned papermaking felts for molding or embossing a web during papermaking, and the method of their use.
In the manufacture of paper products, particularly tissue sheets, it is generally desirable to provide a final product with as much bulk as possible without compromising other product attributes. Many papermaking machines utilize a process known as xe2x80x9cwet-pressing.xe2x80x9d Fundamentally, in xe2x80x9cwet-pressing,xe2x80x9d a large amount of water is removed from the newly-formed web of paper by mechanically pressing water out of the web, while the web is supported on a papermaking felt, in a pressure nip. The pressure nip is formed between the pressure roll and a Yankee dryer surface as the web is transferred from a papermaking felt to the Yankee dryer. The web may then be creped to soften it and provide stretch to the resulting tissue sheet. A disadvantage of the pressing step is that the pressing step may densify the web, thereby decreasing the bulk and absorbency of the tissue sheet. The subsequent creping step may only partially restore the desired sheet properties. This wet-pressing step, while an effective dewatering means, may compress the web and causes a marked reduction in web thickness and hence bulk.
Papermaking felts may be used to remove the water expelled from the web during the wet-pressing operation. One improvement to conventional felts is the application of a pattern to the felt. The pattern is imprinted into the tissue sheet, thereby producing a corresponding high density pattern in the paper. Generally, in the past, the corresponding high density pattern occurs in the X-Y direction, i.e., within the plane of the paper, in almost all cases, the tensile strength of the paper increases with its density.
One manner in which to apply a pattern layer to a papermaking felt is described in U.S. Pat. No. 5,693,187 issued to Ampulski et al. The pattern layer is created by applying a liquid precursor, typically a curable resin, to the felt. Prior to curing, this liquid precursor permeates the felt. The desired portion of the resin is cured, typically through a patterned mask, to form a solid pattern layer. Any excess liquid resin is removed. Such permeation of the liquid precursor into the felt joins the patterned layer to the felt upon curing.
However, this approach, without more, does not control where the liquid precursor, and hence ultimately after curing, the patterned layer permeates the felt. If too much of the liquid which forms the patterned layer permeates the felt and later cures, the felt becomes impermeable. An impermeable felt is undesirable because it does not allow for water removal from the wet web which is in contact with the felt.
Other patterned papermaking felts are generally made with various hardnesses of yarns woven into the felt material as generally disclosed in U.S. Pat. No. 4,533,437 to Curran et. al. The hard yarns in the felt, when pressed against the web during drying, provide for varying densities in the resulting paper produced. The approach disclosed in Curran et. al. is limited by the indirect contact of the yarns with the sheet and the patterns that can be woven using the yarns. Hence, the felts generally disclosed in Curran et al. have only limited ability to influence sheet bulk and are unable to impart aesthetically pleasing patterns to the sheet.
The present invention provides new and non-obvious patterned felts for embossing a pattern onto a tissue sheet and methods for imparting bulk and/or visual aesthetics to a tissue sheet. Individual tissue sheets are the building blocks of tissue products. Tissue products include, but are not limited to, facial tissue, bath tissue, and paper towels or the like. A first aspect of the invention is directed to the combination of a felt substrate for pressing a pattern onto a tissue sheet joined to a raised patterned layer. The felt substrate is joined to the raised patterened layer by an attachment mechanism.
In a second aspect of the invention, there may also be embodied a method for making a tissue sheet having increased bulk and visual aesthetics using a raised pattern felt including the steps of pressing the web with a patterned felt so that the pattern becomes inherent in the sheet. In order to accomplish this, the felt is produced, with a design, such as a butterfly, embroidered or otherwise stitched into the raised pattern layer. A bonding coating, such as a foam, may be applied over the raised pattern layer, the pattern being evident in the bonding coating. In one embodiment, xe2x80x9cpatternedxe2x80x9d may mean having a plurality of projections from the web-contacting surface of the carrier which may be arranged in a manner so as to form a design or pattern. As the web is pressed into the felt substrate joined with the patterned foam layer, the pattern displaces fibers in the sheet, effectively inducing the pattern in the web. The degree of bulk or visual aesthetics imparted to the web is dependent on web weight, sheet consistency, bonding coating layer, and nip pressure. Increasing nip pressure and decreasing sheet consistency may effect bulk or visual aesthetics. Further, the degree of bulk or visual aesthetics may also be influenced by larger patterns extending into the z direction, the direction perpendicular to the plane of the felt.
One advantage of a preferred embodiment of the invention is that the patterned felts can impart significantly increased bulk, increased flexibility, and a high absorbent capacity to the resulting tissue product. These improved properties are largely due to the height, orientation, and arrangement of the resulting protrusions in the sheet due to the felt having a patterned layer thereon. All of these properties are desirable for tissue products. The tissue sheets made in accordance with this invention can be used for one-ply or multiple-ply tissue products.
One advantage of an embodiment of the present invention is the addition of bulk and visual aesthetics to a tissue product. A further advantage of an embodiment of the present invention is that the resulting tissue product has an increase in bulk without a reduction in tensile strength of the tissue product.
A further advantage of one embodiment of the invention is to provide a method for adding bulk and visual aesthetics to a tissue product through a patterned layer joined to the felt without having to change any other machine clothing, equipment, or critical process values.
The invention will be better understood in light of the attached drawings and detailed description of the invention.